A scanning probe microscope is a microscope capable of acquiring a high magnification observation image of a sample surface by detecting any interaction between a probe and a sample while scanning the sample surface with a minute probe. Scanning probe microscopes include a scanning tunneling microscope (STM) that detects an electrical current flowing between a probe and a sample as an interaction and an atomic force microscope (AFM) that detects an atomic force acting between a probe and a sample as an interaction.
A basic configuration of a detection part of a conventionally known AFM is shown in FIG. 6 (see, Patent Document 1, etc.). A sample 10 to be observed is held on a sample stand 12 provided on a substantially cylindrical piezoelectric scanner 11. This piezoelectric scanner 11 includes an XY scanner 11a for moving the sample 10 in two directions of the X-axis and the Y-axis perpendicular to each other, and a Z scanner 11b for minutely moving in Z-axis direction perpendicular to the X-axis and the Y-axis. These scanners 11a and 11b are each equipped with a piezoelectric element (piezo element) that causes a displacement in a predetermined range by a voltage applied from an outside as a driving source. Above the sample 10, a cantilever 13 equipped with a probe 14 at the tip end is arranged. When the tip end of the sharp probe 14 attached to the cantilever 13 is brought close to the proximity (gap of a few nm or less) to the sample 10, an atomic force (attraction force or repulsion force) acts between the tip end of the probe 14 and the atoms of the sample 10. In this state, while scanning the sample surface by the piezoelectric scanner 11 so that the probe 14 and the sample 10 move relatively in the X-Y plane, the distance (in the Z-axis direction, or height) of the probe 14 from the sample 10 is feedback controlled so that the atomic force is kept constant. The feedback amount in the Z-axis direction corresponds to the irregularity of the surface of the sample. Therefore, based on this, a three-dimensional image of the sample surface can be obtained.
In the configuration of FIG. 6, to detect the displacements of the cantilever 13 in the Z-axis direction, a photometric unit 20 is provided above the cantilever 13. That is, the laser light emitted from the laser diode 15 is converged by the lens 16 and then reflected by the beam splitter 17 to be irradiated to the vicinity of the tip end of the cantilever 13. Then, the reflected light is detected by the light detector 19 via the mirror 18. The light detector 19 includes light receiving surfaces divided into plural (normally, two or four) sections in the displacement direction (Z-axis direction) of the cantilever 13. Since the ratio of the amount of incident light to the plurality of light receiving surfaces changes when the cantilever 13 is displaced up or down, the displacement amount of the cantilever 13 can be calculated by performing the calculation processing of the detection signal corresponding to the plurality of light-receiving amounts.